Systems and methods of monitoring a thermal protection system

ABSTRACT

A method of monitoring a thermal protection system coupled to a structural component is provided. The thermal protection system includes a thermally insulative body and at least one layer of thermochromatic material applied thereon such that the at least one layer is positioned between the thermally insulative body and the structural component. The method includes determining a value of a thermochromatic property of the at least one layer of thermochromatic material, wherein the value of the thermochromatic property is responsive to an amount of heat applied to the at least one layer of thermochromatic material, comparing the value to a baseline value of the thermochromatic property, and determining degradation of the thermal protection system when the value of the thermochromatic property deviates from the baseline value.

BACKGROUND

The field of the present disclosure relates generally to thermalprotection systems and, more specifically, to using thermochromaticcoatings to monitor the structural integrity of thermal protectionsystems.

Thermal protection systems are generally implemented in the aerospaceindustry to thermally shield reusable launch vehicles (RLVs) from hightemperatures caused by re-entry into Earth's atmosphere, or on certainaircraft in locations downstream from high-temperature engine exhaust,for example. At least some known thermal protection systems are formedfrom a heat-resistant fabric that facilitates maintaining a temperatureof a metallic and/or composite structural of the vehicle below thethermal protection system. At least some known heat-resistant fabricsare fabricated from fiberglass, Nomex®, Kevlar®, and combinationsthereof.

While generally effective at thermally shielding structural componentsof a vehicle, at least some known heat-resistant fabrics have a limitedservice life. For example, heat-resistant properties of theheat-resistant fabrics may degrade over time resulting in damage to theunderlying structural components. At least some known non-destructiveexamination (NDE) techniques are capable of determining degradation ofheat-resistant fabrics. However, such techniques are generallytime-consuming and may be unable to detect degradation in theheat-resistant blanket until at least some damage to the underlyingstructural components has occurred.

BRIEF DESCRIPTION

In one aspect, a method of monitoring a thermal protection systemcoupled to a structural component is provided. The thermal protectionsystem includes a thermally insulative body and at least one layer ofthermochromatic material applied thereon such that the at least onelayer is positioned between the thermally insulative body and thestructural component. The method includes determining a value of athermochromatic property of the at least one layer of thermochromaticmaterial, wherein the value of the thermochromatic property isresponsive to an amount of heat applied to the at least one layer ofthermochromatic material, comparing the value to a baseline value of thethermochromatic property, and determining degradation of the thermalprotection system when the value of the thermochromatic propertydeviates from the baseline value.

In another aspect, a thermal protection system is provided. The systemincludes a thermally insulative body and at least one layer ofthermochromatic material applied to the thermally insulative body. Avalue of a thermochromatic property of the at least one layer ofthermochromatic material is responsive to an amount of heat applied tothe at least one layer of thermochromatic material.

In yet another aspect, a system for use in monitoring a thermalprotection system is provided. The thermal protection system includes athermally insulative body and at least one layer of thermochromaticmaterial applied thereon. The system includes at least one moduleincluding a substrate coupled to the at least one layer ofthermochromatic material, an excitation source coupled to the substrateand configured to direct light towards the at least one layer, and adetection system coupled to the substrate and configured to receive asignal emitted from the at least one layer. The signal includes a valueof a thermochromatic property of the at least one layer. A controller isin communication with the at least one module, and is configured todirect the excitation source to selectively direct light towards the atleast one layer, and receive the signal from the detection system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of an exemplary aircraft production and servicemethod.

FIG. 2 is a block diagram of an exemplary aircraft.

FIG. 3 is a schematic cross-sectional illustration of an exemplarythermal protection system.

FIG. 4 is a schematic illustration of an exemplary monitoring systemthat may be used with the thermal protection system shown in FIG. 3.

FIG. 5 is a schematic illustration of the thermal protection systemshown in FIG. 3 utilizing the monitoring system shown in FIG. 4.

FIG. 6 is a flow diagram of an exemplary method of monitoring a thermalprotection system that may be used with the thermal protection systemshown in FIG. 3.

DETAILED DESCRIPTION

The implementations described herein relate to systems and methods ofmonitoring thermal protection systems. In an exemplary implementation,the thermal protection system is coupled to a structural component andincludes a thermally insulative body and at least one layer ofthermochromatic material applied to an underside of the thermallyinsulative body such that the layer is positioned between the thermallyinsulative body and the structural component. The thermochromaticmaterial is responsive to changes in temperature such that a value of athermochromatic property of the layer permanently shifts when an excessamount of heat is conducted through the thermally insulative body. Morespecifically, the value only shifts when the temperature of the layer isgreater than a predetermined threshold, which provides a visualindication of potential degradation of the thermal protection system.Also described herein is a micro-opto-electro-mechanical system (MOEMS)capable of detecting shifts in the value while the thermal protectionsystem remains in-situ.

Referring to the drawings, implementations of the disclosure may bedescribed in the context of an aircraft manufacturing and service method100 (shown in FIG. 1) and via an aircraft 102 (shown in FIG. 2). Duringpre-production, including specification and design 104 data of aircraft102 may be used during the manufacturing process and other materialsassociated with the airframe may be procured 106. During production,component and subassembly manufacturing 108 and system integration 110of aircraft 102 occurs, prior to aircraft 102 entering its certificationand delivery process 112. Upon successful satisfaction and completion ofairframe certification, aircraft 102 may be placed in service 114. Whilein service by a customer, aircraft 102 is scheduled for periodic,routine, and scheduled maintenance and service 116, including anymodification, reconfiguration, and/or refurbishment, for example. Inalternative implementations, manufacturing and service method 100 may beimplemented via vehicles other than an aircraft.

Each portion and process associated with aircraft manufacturing and/orservice 100 may be performed or completed by a system integrator, athird party, and/or an operator (e.g., a customer). For the purposes ofthis description, a system integrator may include without limitation anynumber of aircraft manufacturers and major-system subcontractors; athird party may include without limitation any number of venders,subcontractors, and suppliers; and an operator may be an airline,leasing company, military entity, service organization, and so on.

As shown in FIG. 2, aircraft 102 produced via method 100 may include anairframe 118 having a plurality of systems 120 and an interior 122.Examples of high-level systems 120 include one or more of a propulsionsystem 124, an electrical system 126, a hydraulic system 128, and/or anenvironmental system 130. Any number of other systems may be included.

Apparatus and methods embodied herein may be employed during any one ormore of the stages of method 100. For example, components orsubassemblies corresponding to component production process 108 may befabricated or manufactured in a manner similar to components orsubassemblies produced while aircraft 102 is in service. Also, one ormore apparatus implementations, method implementations, or a combinationthereof may be utilized during the production stages 108 and 110, forexample, by substantially expediting assembly of, and/or reducing thecost of assembly of aircraft 102. Similarly, one or more of apparatusimplementations, method implementations, or a combination thereof may beutilized while aircraft 102 is being serviced or maintained, forexample, during scheduled maintenance and service 116.

As used herein, the term “aircraft” may include, but is not limited toonly including, airplanes, unmanned aerial vehicles (UAVs), gliders,helicopters, and/or any other object that travels through airspace.Further, in an alternative implementation, the aircraft manufacturingand service method described herein may be used in any manufacturingand/or service operation.

FIG. 3 is a schematic cross-sectional illustration of an exemplarythermal protection system 200. In an exemplary implementation, thermalprotection system 200 is coupled to a structural component 202 ofaircraft 102 (shown in FIG. 2). Thermal protection system 200 includes athermally insulative body 204 including a first surface 206 and a secondsurface 208. Thermal protection system 200 facilitates shieldingstructural component 202 from potential heat damage when structuralcomponent 202 and thermal protection system 200 are exposed to a firstamount 210 of heat. For example, while thermal protection system 200 mayinhibit heat transfer from first surface 206 to second surface 208, someamount of heat (e.g., a second amount 212 of heat) may reach secondsurface 208. Second amount 212 of heat may be conducted throughthermally insulative body 204 from first surface 206. In someimplementations, second amount 212 of heat reaches second surface 208due to gaps in and/or around thermally insulative body 204, and/ordisplacement or movement of thermally insulative body 204 relative tostructural component 202. At least one layer 214 of thermochromaticmaterial is applied to second surface 208 such that layer 214 ofthermochromatic material is positioned between thermally insulative body204 and structural component 202. As will be described in more detailbelow, layer 214 of thermochromatic material facilitates providing avisual indication of potential heat damage to structural component 202and/or degradation of thermally insulative body 204, which may be causedby second amount 212 of heat.

Thermally insulative body 204 may be fabricated from any material thatenables thermal protection system 200 to function as described herein.For example, in an exemplary implementation, thermally insulative body204 is a woven or non-woven material formed from a plurality ofheat-resistant fibers 216. Exemplary heat-resistant fibers 216 include,but are not limited to, fiberglass, Nomex® fibers, and Kevlar® fibers.(“Nomex” and “Kevlar” are both registered trademarks of E.I. du Pont deNemours and Company of Wilmington, Del.).

Layer 214 of thermochromatic material may be fabricated from anythermochromatic material that enables thermal protection system 200 tofunction as described herein. For example, in an exemplaryimplementation, the thermochromatic material is fabricated from one ormore thermochromatic dyes responsive to temperatures above apredetermined threshold. More specifically, a value of a thermochromaticproperty of the thermochromatic material is responsive to an amount ofheat applied to layer 214 of thermochromatic material or that isconducted through thermally insulative body 204. Moreover, in oneimplementation, the thermochromatic material includes photoluminescentmaterial. As such, the thermochromatic property is only visible to thehuman eye when activated by non-visible light such that a shift in avalue of the thermochromatic property cannot be seen by a casualobserver (not shown). Exemplary thermochromatic properties include atleast one of an intensity or a frequency of light emitted from layer 214of thermochromatic material.

In operation, thermal protection system 200 is exposed to first amount210 of heat, such as heat from a flow of exhaust gas discharged fromaircraft 102 (shown in FIG. 2), and thermally insulative body 204facilitates shielding structural component 202 from the heat. However,thermally insulative body 204 may degrade during the service life ofaircraft 102 such that second amount 212 of heat conducts throughthermally insulative body 204 towards structural component 202.Alternatively, second amount 212 of heat may reach second surface 208through gaps (not shown) in thermally insulative body 204, and/ormovement of thermally insulative body 204 relative to structuralcomponent 202. Layer 214 of thermochromatic material is responsive tothe amount of heat that reaches second surface 208 and facilitatesdetermining degradation of thermally insulative body 204 as a resultthereof.

In an exemplary implementation, a value of a thermochromatic property oflayer 214 is only modified to a different level when a temperature oflayer 214 is greater than a predetermined threshold. For example, thethermochromatic property across layer 214 has a substantially uniformbaseline value when the temperature of layer 214 is below thepredetermined threshold, and the value of the thermochromatic propertyis permanently modified to be at a different level when the temperatureof layer 214 is greater than the predetermined threshold. Morespecifically, the value of the thermochromatic property is modified tothe different level, and the value remains at the different level evenafter the temperature of layer 214 reduces to below the predeterminedthreshold. In one implementation, the value of the thermochromaticproperty is modified to a plurality of different levels as thetemperature of layer 214 progressively increases above the predeterminedthreshold. As such, second amount 212 of heat that reaches secondsurface 208 can be determined based on which level the value hasreached. The second amount 212 of heat may be directly proportional toan amount of degradation of thermally insulative body 204.

In some implementations, the value of the thermochromatic property ispermanently modified such that thermal protection system 200 can beinspected at safe temperatures below the predetermined threshold. Forexample, to be inspected at predetermined service intervals, thermalprotection system 200 is at least partially removed from structuralcomponent 202 such that layer 214 is exposed, and the value of thethermochromatic property of layer 214 is determined. More specifically,in one implementation, non-visible light (e.g., ultraviolet or infraredlight) is directed towards exposed layer 214 and the photoluminescentmaterial in layer 214 absorbs the non-visible light. Light is emittedfrom layer 214 at an intensity and/or frequency after the non-visiblelight has been removed. The value of the intensity and/or frequency ofthe emitted light is then compared to a baseline intensity and/orfrequency value, and potential heat damage is located at second surface208 when the value deviates from the baseline intensity and/or frequencyvalue. For example, in one implementation, potential deviations from thebaseline value are determined using image analysis software.

FIG. 4 is a schematic illustration of an exemplary monitoring system217, and FIG. 5 is a schematic illustration of thermal protection system200 utilizing the monitoring system 217. In the exemplaryimplementation, monitoring system 217 includes amicro-opto-electro-mechanical system (MOEMS) module 218 and a controller220 coupled in communication with MOEMS module 218. MOEMS module 218includes a substrate 222, an excitation source 224 coupled to substrate222, a fiber laser excitation delivery system 226 in communication withexcitation source 224, a detection system 228 coupled to substrate 222,and power/data delivery conduits 230 in communication with detectionsystem 228. Excitation source 224 includes a light source such as alight-emitting diode (not shown), and detection system includes aplurality of light sensors 232 that each detect light in differentspectral ranges. Moreover, in some implementations, MOEMS module 218includes a filter 234, such as a color filter or a narrow bandwithfilter, that facilitates restricting frequencies of light received bydetection system 228. In an alternative implementation, conduits 230 areomitted from MOEMS module 218 and signals received by detection system228 are provided to controller 220 wirelessly.

Referring to FIG. 5, layer 214 includes a plurality of portions 236 eachapplied to a predetermined region 238 of thermally insulative body 204.Each predetermined region 238 corresponds to areas across second surface208 known to be most susceptible to degradation. A plurality of modules(e.g., MOEMS modules 218) may be coupled to layer 214 at plurality ofportions 236. For example, MOEMS modules 218 are coupled to each portion236 of layer 214 such that a value of light emitted from each portion236 can be determined MOEMS modules 218 are coupled to layer 214 with anadhesive (not shown), for example, and are positioned between layer 214and structural component 202 (shown in FIG. 3). In an alternativeimplementation, layer 214 may be applied across the entirety of secondsurface 208 and MOEMS modules 218 may be positioned at predeterminedregions 238.

In operation, controller 220 directs excitation source 224 toselectively direct light towards layer 214 of thermochromatic material.Controller 220 substantially synchronizes operation of excitation source224 and detection system 228 such that excitation source 224 onlydirects light towards layer 214 while detection system 228 is capturingdata. Detection system 228 then receives a signal (not shown) emittedfrom layer 214, and controller 220 receives the signal. The signalincludes the value of a thermochromatic property of layer 214.Controller 220 then compares the value to a baseline value of thethermochromatic property and determines degradation of thermallyinsulative body 204 when the value of the thermochromatic propertydeviates from the baseline value. As such, monitoring system 217 enablesin-situ monitoring of thermal protection system 200 without having toremove thermally insulative body 204 from structural component 202.

FIG. 6 is a flow diagram of an exemplary method 300 of monitoring athermal protection system that may be used with thermal protectionsystem 200 (shown in FIG. 3). In an exemplary implementation, method 300includes coupling 302 thermal protection system 200 to structuralcomponent 202, exposing 304 structural component 202 with thermalprotection system 200 thereon to heat, and at least partially removing306 thermal protection system 200 from structural component 202.Non-visible light is then directed 308 towards layer 214 ofthermochromatic material applied to an underside of thermal protectionsystem 200. Method 300 also includes determining 310 a value of athermochromatic property of the thermochromatic material, comparing 312the value to a baseline value of the thermochromatic property, anddetermining 314 degradation of thermal protection system 200 based on adeviation between the value of the thermochromatic property and thebaseline value.

The implementations described herein relate to systems and methods ofmonitoring thermal protection systems to facilitate detectingdegradation thereof before damage to an underlying structural can occur.In the exemplary implementation, at least one layer of thermochromaticmaterial is positioned between a thermally insulative body and theunderlying structural. As the thermally insulative body degrades, theamount of heat conducted through the thermally insulative body towardsthe underlying structural increases. The layer of thermochromaticmaterial facilitates detecting hot spots on the underside of thethermally insulative body by providing a visual indication at locationsof potential degradation of the thermally insulative body. Thethermochromatic material is selected to be selectively responsive totemperatures indicative of potential degradation, and is selected suchthat the visual indication remains even when the temperature of thelayer returns to a safe inspection level. As such, the systems andmethods described herein enable the structural integrity of thethermally insulative body to be determined in an efficient andcost-effective manner.

This written description uses examples to disclose variousimplementations, including the best mode, and also to enable any personskilled in the art to practice the various implementations, includingmaking and using any devices or systems and performing any incorporatedmethods. The patentable scope of the disclosure is defined by theclaims, and may include other examples that occur to those skilled inthe art. Such other examples are intended to be within the scope of theclaims if they have structural elements that do not differ from theliteral language of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal language of theclaims.

What is claimed is:
 1. A method of monitoring a thermal protectionsystem coupled to a structural component, the thermal protection systemincluding a thermally insulative body and at least one layer ofthermochromatic material applied thereon such that the at least onelayer is positioned between the thermally insulative body and thestructural component, the method comprising: determining a value of athermochromatic property of the at least one layer of thermochromaticmaterial, wherein the value of the thermochromatic property isresponsive to an amount of heat applied to the at least one layer ofthermochromatic material; comparing the value to a baseline value of thethermochromatic property; and determining degradation of the thermalprotection system when the value of the thermochromatic propertydeviates from the baseline value.
 2. The method in accordance with claim1, wherein determining a value comprises determining the value of atleast one of an intensity or a frequency of light emitted from the atleast one layer of thermochromatic material.
 3. The method in accordancewith claim 1, wherein determining a value comprises determining aplurality of values of the thermochromatic property, each of theplurality of values corresponding to a predetermined region of the atleast one layer of thermochromatic material.
 4. The method in accordancewith claim 1 further comprising directing non-visible light towards theat least one layer of thermochromatic material, wherein thethermochromatic material includes photoluminescent material configuredto be activated by the non-visible light.
 5. The method in accordancewith claim 4 further comprising at least partially removing the thermalprotection system from the structural component to expose the at leastone layer of thermochromatic material to the non-visible light.
 6. Themethod in accordance with claim 1, wherein comparing the value comprisesselecting the baseline value that corresponds to a temperature of the atleast one layer below a predetermined threshold.
 7. A thermal protectionsystem comprising: a thermally insulative body; and at least one layerof thermochromatic material applied to the thermally insulative body,wherein a value of a thermochromatic property of the at least one layerof thermochromatic material is responsive to an amount of heat appliedto the at least one layer of thermochromatic material.
 8. The system inaccordance with claim 7, wherein the at least one layer ofthermochromatic material includes photoluminescent material configuredto be activated by non-visible light.
 9. The system in accordance withclaim 7, wherein the at least one layer of thermochromatic material isconfigured such that the value of the thermochromatic property ismodified to a different level when a temperature of the at least onelayer is greater than a predetermined threshold.
 10. The system inaccordance with claim 9, wherein the at least one layer ofthermochromatic material is configured such that the value of thethermochromatic property remains at the different level when thetemperature of the at least one layer reduces to below the predeterminedthreshold.
 11. The system in accordance with claim 9, wherein the atleast one layer of thermochromatic material is configured such that thevalue of the thermochromatic property is modified to a plurality ofdifferent levels as the temperature of the at least one layerprogressively increases above the predetermined threshold.
 12. Thesystem in accordance with claim 7, wherein the at least one layer ofthermochromatic material is configured such that the value of thethermochromatic property is substantially uniform across the at leastone layer when the temperature of the at least one layer is less than apredetermined threshold.
 13. The system in accordance with claim 7,wherein the at least one layer of thermochromatic material includes aplurality of portions each applied to a predetermined region of thethermally insulative body.
 14. The system in accordance with claim 7,wherein the thermally insulative body is fabricated from a plurality ofheat-resistant fibers.
 15. A system for use in monitoring a thermalprotection system including a thermally insulative body and at least onelayer of thermochromatic material applied thereon, the systemcomprising: at least one module comprising: a substrate coupled to theat least one layer of thermochromatic material; an excitation sourcecoupled to the substrate and configured to direct light towards the atleast one layer; and a detection system coupled to the substrate andconfigured to receive a signal emitted from the at least one layer, thesignal including a value of a thermochromatic property of the at leastone layer; and a controller in communication with the at least onemodule, the controller configured to: direct the excitation source toselectively direct light towards the at least one layer; and receive thesignal from the detection system.
 16. The system in accordance withclaim 15, wherein the at least one module comprises a plurality ofmodules each coupled to a predetermined region of the thermallyinsulative body.
 17. The system in accordance with claim 15, wherein theat least one module comprises at least one filter configured to restrictfrequencies of light received by the detection system.
 18. The system inaccordance with claim 15, wherein the detection system comprises aplurality of light sensors that each detect light in different spectralranges.
 19. The system in accordance with claim 15, wherein thecontroller is further configured to: compare the value of thethermochromatic property to a baseline value of the thermochromaticproperty; and indicate degradation of the thermally insulative body ifthe value of the thermochromatic property deviates from the baselinevalue.
 20. The system in accordance with claim 15, wherein thecontroller is further configured to determine the value of at least oneof an intensity or a frequency of the signal emitted from the at leastone layer of thermochromatic material.